The lipases' high regio- and enantioselectivity, activity inorganic solvent and environmentally compatible reactionconditions have made lipase-catalysis based synthesis anattractive alternative to conventional synthetic methods inorganic chernistry and a new synthetic tool in polymerchemistry.
The regioselective acylation of methy1 glycopyranosides wereinvestigated using several serine hydrolases. All activelipases preferentiahy acylated the primary alcohol group of themethy1 glycopyranosides. There were two tonfiguration effectscontributing to the acylation rate and hence enzymespecificity, namely the equatoriali axial position of thesecondary alcohol grottps and the anomeric tonfiguration. Whichone of the two effects that had the greatest impact on theacylation rate depended on the lipase species.
The lipaseBderived from theyeast Cundida unturcticawas shown to be a very efftcient catalyst in the synthesisof poly(&-caprolactone) (PCL). The highest average Mwand fastest polymerisation rate was obtained whenthe polymerisation was conducted without solvent, bulkpolymerisation. In organic solvent, at high dilution, C.anturcticu lipase B formed macrocycles of up to 196 atoms,which are the largest macrocycles synthesised by lipasecatalysis so far reported.
C.anturcticalipaseBwas efftcient in combining the regioselectiveacylation of polyols and polyester synthesis. For examplemethy1 6-0-poly(&-caprolactone)glycopyranosides and apoly(&-caprolactone) mono substituted furst generationdendrimer were synthesised.
Based on the mechanism of lipase-catalysed ring-openingpolymerisation synthetic strategies to obtain variousend-functionaliscd PCL by initiation and termination reactionswere developed. In the termination reaction, the importante ofhaving a fast reacting acyl donor was elucidated. If this wasnot the case the PCL could att as the acyl donor instead ofbeing the acyl acceptor. The end-functionalised products weredesigned to be used as starting materials for furthertransformations by biocatalysis or chemical catalysis toproduce novel materials.
Keywords:lipase, catalysis, regioselectivity,specificity, ring-opening polymerisation,poly(&-caprolactone), macrocycles,Candida antarctica,methy1 glycopyranosides, end-group functionalisations,matromonomers, initiation, termination.
Stockholm: Bioteknologi , 1998. , 38 p.